The proposed study will investigate the effects on nephron function of a) tubular obstruction and b) intraluminal serum infusion. Experiments will be done in anesthetized rats, using micropuncture techniques. Specific goals will be (1) to examine the effects of 24-hour distal nephron blockade on glomerular capillary pressure, (2) to examine the effect of uremia on the response to tubule obstruction, (3) to examine the effects of renin-angiotensin and thromboxane inhibitors on the afferent arteriolar vasoconstriction which develops with chronic tubule blockade, and (4) to study the morphology of tubules blocked for various times with solid paraffin. These studies should elucidate the mechanisms involved in the decreased glomerular function that occurs with chronic tubule blockade. Intraluminal infusion of fresh serum may produce proximal tubule damage. Experiments to be done will look at the specificity of this response and will determine whether tubule damage leads to changes in glomerular function.